DI-27
10
Key Design Points
• Design bias winding circuit to provide 250 µA to 300 µA
at no-load.
• Ensure C5 is large enough to supply above current at the
very low no-load switching frequencies.
• Minimize secondary circuit bias currents. Use low current
feedback Zeners for best tolerance.
• ZenerorRCDclampcanbeusedtoslightlyreduceno-load
consumption further. Use a 200 V Zener or maximize
resistor value in RCD clamp for lowest losses.
• Designtransformerwithlowreflectedvoltagetominimize
clamp losses.
• Wind transformer for lowest leakage inductance. Choose
wire gauges to completely fill winding layers.
• Wind transformer with tape between primary layers to
further reduce intra-winding capacitance.
8
6
4
2
Zener Clamp
RC Clamp
0
80
120
160
200
240
AC Line Voltage (A)
Figure 3. No-load Input Power Variation with Input Voltage.
100
TRANSFORMER PARAMETERS
VIN = 100 VAC
VIN = 230 VAC
EE16
Nippon Ceramic NC-2H
AL of 74 nH/T2
Core Material
Bobbin
EE16 10 pin
(Ying Chin YC1607 or equivalent)
10
Primary (1-2), Tape
12 V (10-9), Tape
Bias (3-4), Tape
Winding Order
(pin numbers)
Primary Inductance
3.67 mH ±10%
500 kHz (minimum)
300 µH (maximum)
Primary Resonant
Frequency
1
0
100
200
300
400
500
Leakage Inductance
BYPASS Pin Current (µA)
Figure 2. No-load Input Power vs. BYPASS Pin Current.
Table 1. Transformer Construction Information.
For the latest updates, visit our Web site: www.powerint.com
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Power Integrations does not assume any liability arising from the use of any device or circuit described herein, nor does it convey any
license under its patent rights or the rights of others. The products and applications illustrated herein may be covered by one or more U.S.
and foreign patents or potentially by pending U.S. and foreign patent applications assigned to Power Integrations. A complete list of Power
Integrations’ patents may be found at www.powerint.com.
The PI Logo, TOPSwitch, TinySwitch and EcoSmart are registered trademarks of Power Integrations, Inc.
PI Expert is a trademark of Power Integrations, Inc. ©Copyright 2002, Power Integrations, Inc.
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